Methods providing signal synchronization and related networks and devices

ABSTRACT

A method of providing signal synchronization for a radio access network may include transmitting a first carrier including synchronization signals on a first frequency from the radio access network. Information relating the first carrier on the first frequency with a second carrier on a second frequency may be transmitted from the radio access network, with this information being intended to be used in synchronization by a wireless terminal upon addition of the second carrier. More particularly, the first and second frequencies may be different. A command to add the second carrier as a downlink for transmissions may be transmitted to the wireless terminal. Related network nodes and wireless terminals are also discussed.

RELATED APPLICATIONS

The present application claims the benefit of priority from U.S.Provisional Application No. 61/373,969 entitled “Methods And ApparatusFor Signaling Synchronization” filed Aug. 16, 2010, the disclosure ofwhich is hereby incorporated herein in its entirety by reference.

BACKGROUND

In a typical cellular radio system, wireless terminals (also known asmobile stations and/or user equipment units (UEs)) communicate via aradio access network (RAN) to one or more core networks. User equipmentunits may include mobile telephones (“cellular” telephones) and/or otherprocessing devices with wireless communication capability, such as, forexample, portable, pocket, hand-held, laptop computers, whichcommunicate voice and/or data with the RAN.

The RAN covers a geographical area which is divided into cell areas,with each cell area being served by a base station, e.g., a radio basestation (RBS), which in some networks is also called a “NodeB” orenhanced NodeB “eNodeB”, which can be abbreviated “eNB.” A cell area isa geographical area where radio coverage is provided by the radio basestation equipment at a base station site. The base stations communicateover the air interface operating on radio frequencies with UEs withinrange of the base stations.

In some versions of the radio access network, several base stations aretypically connected (e.g., by landlines or microwave) to a radio networkcontroller (RNC). The radio network controller, also sometimes termed abase station controller (BSC), supervises and coordinates variousactivities of the plural base stations connected thereto. The radionetwork controllers are typically connected to one or more corenetworks.

The Universal Mobile Telecommunications System (UMTS) is a thirdgeneration mobile communication system, which evolved from the GlobalSystem for Mobile Communications (GSM), and is intended to provideimproved mobile communication services based on Wideband Code DivisionMultiple Access (WCDMA) access technology. UTRAN, short for UMTSTerrestrial Radio Access Network, is a collective term for the Node B'sand Radio Network Controllers which make up the UMTS radio accessnetwork. Thus, UTRAN is essentially a radio access network usingwideband code division multiple access for user equipment units.

The Third Generation Partnership Project (3GPP) has undertaken to evolvefurther the UTRAN and GSM based radio access network technologies. Inthis regard, specifications for the Evolved Universal Terrestrial RadioAccess Network (E-UTRAN) are ongoing within 3GPP. The Evolved UniversalTerrestrial Radio Access Network (E-UTRAN) comprises the Long TermEvolution (LTE) and System Architecture Evolution (SAE).

FIG. 1 is a simplified block diagram of a Long Term Evolution (LTE) RAN100. The LTE RAN 100 is a variant of a 3GPP RAN where radio base stationnodes (eNodeBs) are connected directly to a core network 130 rather thanto radio network controller (RNC) nodes. In general, in LTE thefunctions of a radio network controller (RNC) node are performed by theradio base stations nodes. Each of the radio base station nodes(eNodeBs) 122-1, 122-2, . . . 122-M communicate with UEs (e.g., UE110-1, 110-2, 110-3, . . . 110-L) that are within their respectivecommunication service cells. The radio base station nodes (eNodeBs) cancommunicate with one another through an X2 interface and with the corenetwork 130 through S1 interfaces, as is well known to one who isskilled in the art.

The LTE standard is based on multi-carrier based radio access schemessuch as Orthogonal Frequency-Division Multiplexing (OFDM) in thedownlink and Discrete Fourier Transform (DFT)-spread OFDM in the uplink.The OFDM technique distributes the data over a large number of carriersthat are spaced apart at precise frequencies. This spacing provides the“orthogonality” in this technique which avoids having demodulators seefrequencies other than their own. The benefits of OFDM are high spectralefficiency, resiliency to RF interference, and lower multi-pathdistortion.

FIG. 2 illustrates a resource grid for frequency and time resourceelements (REs), where each resource element corresponds to one OFDMsubcarrier during one OFDM symbol interval. In the time domain, LTEdownlink transmissions may be organized into radio frames of 10 ms, andeach radio frame may consist of ten equally-sized subframes of lengthT_(subframe)=1 ms, as illustrated in FIG. 3.

One or more resource schedulers in the LTE RAN 100 allocate resourcesfor uplink and downlink in terms of resource blocks, where a resourceblock corresponds to one slot (0.5 ms) in the time domain and 12subcarriers in the frequency domain. Resource blocks are numbered in thefrequency domain, starting with 0 from one end of the system bandwidth.

The LTE Rel-8 standard has recently been standardized, supportingbandwidths up to 20 MHz. 3GPP has initiated work on LTE Rel-10 in orderto support bandwidths larger than 20 MHz and support other requirementsdefined by IMT-Advanced Requirements. Another requirement for LTE Rel-10is to provide backward compatibility with LTE Rel-8, including spectrumcompatibility. This requirement may cause an LTE Rel-10 carrier toappear as a number of LTE carriers to an LTE Rel-8 terminal. Each suchcarrier can be referred to as a Component Carrier (CC). In particularfor early LTE Rel-10 deployments it can be expected that there will be asmaller number of LTE Rel-10-capable terminals compared to many LTElegacy terminals. Therefore, it can be particularly important to ensureefficient use of the wide carrier by legacy terminals, such as byenabling legacy terminals to be scheduled in all parts of the widebandLTE Rel-10 carrier. One way to obtain this may be by means of CarrierAggregation. Carrier Aggregation refers to an LTE Rel-10 terminal beingconfigured to receive multiple CC, where the CC have, or at least thepossibility to have, the same structure as a Rel-8 carrier. The samestructure as Rel-8 implies that all Rel-8 signals, e.g. (primary andsecondary) synchronization signals, reference signals, systeminformation are transmitted on each carrier. FIG. 4 graphicallyillustrates an exemplary 100 MHz Carrier Aggregation of five 20 MHz CCs.

Referring to FIG. 4, the number of aggregated CC as well as thebandwidth of the individual CC may be different for uplink and downlink.A symmetric configuration refers to the case where the number of CCs indownlink and uplink is the same whereas an asymmetric configurationrefers to the case that the numbers of CCs in downlink and uplink aredifferent. It is important to note that the number of CCs offered by thenetwork may be different from the number of CCs seen by a terminal. Forexample, a terminal may support more downlink CCs than uplink CCs, eventhough the network offers the same number of uplink and downlink CCs.

During initial access a LTE Rel-10 terminal may operate similarly to aLTE Rel-8 terminal. Upon successful connection to the network, aterminal may—depending on its own capabilities and the network—beconfigured with additional CCs in the UL and DL. Configuration is basedon Radio Resource Control (RRC). Due to the heavy signaling and ratherslow speed of RRC signaling, a terminal may be configured with multipleCCs even though not all of them are currently used. If a terminal isconfigured for multiple CCs it may have to monitor Physical DownlinkControl Channel (PDCCH) and Physical Downlink Shared Channel (PDSCH) forall DL CCs. However, such terminal configuration may necessitate use ofa wider receiver bandwidth, higher sampling rates, etc. resulting inhigh power consumption.

SUMMARY

According to some embodiments of the present invention, a method ofproviding signal synchronization for a radio access network may includetransmitting a first carrier including synchronization signals on afirst frequency from the radio access network. Information relating thefirst carrier on the first frequency with a second carrier on a secondfrequency may be transmitted from the radio access network, with theinformation being intended to be used in synchronization by the wirelessterminal upon addition of the second carrier. Moreover, the first andsecond frequencies may be different. In addition, a command to add thesecond carrier as a downlink for transmissions may be transmitted to thewireless terminal.

The first and second carriers may be time aligned at the user equipment,and the synchronization signals may be transmitted in periodic resourceelements of the first carrier. The information relating the secondcarrier with the first carrier may include a list of a plurality ofsecond carriers on a respective plurality of second frequencies that arerelated with the first carrier, and/or the information relating thesecond carrier with the first carrier may include a list identifying aplurality of first carriers on a respective plurality of firstfrequencies that are related with the second carrier.

The first carrier may be configured as a downlink to the wirelessterminal, and transmitting the information relating the second carrierwith the first carrier may include transmitting the information over thefirst carrier to the wireless terminal. Transmitting the informationrelating the second carrier with the first carrier may includetransmitting the information to the wireless terminal with the commandto add the second carrier. Transmitting the information relating thesecond carrier with the first carrier may include transmitting theinformation over a third frequency different than the first frequencyand different than the second frequency.

After transmitting the information and the command to add the secondcarrier, acknowledgment may be received from the wireless terminalindicating synchronization and/or configuration of the second carrier atthe wireless terminal. Responsive to receiving the acknowledgment,downlink data may be transmitted over the second carrier to the wirelessterminal.

Transmitting the command to add the second carrier may includetransmitting a flag having one of a first value and a second value. Thefirst value may instruct the wireless terminal to synchronize and/orconfigure the second carrier using the synchronization signals of thefirst carrier, and the second value may instruct the wireless terminalto synchronize and/or configure the second carrier without using thesynchronization signals of the first carrier.

According to some other embodiments of the present invention, signalsynchronization may be provided for a wireless terminal communicatingwith a radio access network that transmits a first carrier includingsynchronization signals on a first frequency. More particularly,information relating a second carrier on a second frequency with thefirst carrier on the first frequency may be received from the radioaccess network, and a command to add the second carrier as a downlinkfor transmissions may be received from the radio access network.Responsive to receiving the command to add the second carrier, thesecond carrier on the second frequency may be synchronized and/orconfigured by the wireless terminal using the synchronization signals ofthe first carrier on the first frequency.

The first and second carriers may be time aligned, and thesynchronization signals may be transmitted by the radio access networkin periodic resource elements of the first carrier. The informationrelating the second carrier with the first carrier may include a list ofa plurality of second carriers on a respective plurality of secondfrequencies that are related with the first carrier, and/or theinformation relating the second carrier with the first carrier mayinclude a list identifying a plurality of first carriers on a respectiveplurality of first frequencies that are related with the second carrier.

The first carrier may be configured as a downlink from the radio accessnetwork to the wireless terminal, and receiving the information relatingthe second carrier with the first carrier may include receiving theinformation over the first carrier at the wireless terminal. Receivingthe information relating the second carrier with the first carrier mayinclude receiving the information at the wireless terminal with thecommand to add the second carrier. Receiving the information relatingthe second carrier with the first carrier may include receiving theinformation over a third frequency different than the first frequencyand different than the second frequency.

Receiving the command to add the second carrier may include receiving aflag having one of a first value and a second value. Synchronizingand/or configuring the second carrier may include synchronizing and/orconfiguring the second carrier using the synchronization signals of thefirst carrier responsive to receiving the flag having the first value,and synchronizing and/or configuring the second carrier without usingthe synchronization signals of the first carrier responsive to receivingthe flag having the second value.

Before receiving the command, a third carrier may be configured on athird frequency as a downlink carrier for transmissions from the radioaccess network to the wireless terminal. Responsive to receiving theflag having the first value, the wireless terminal may synchronizeand/or configure the second carrier on the second frequency using thesynchronization signals of the first carrier on the first frequency.Responsive to receiving the flag having the second value, the wirelessterminal may synchronize and/or configure the second carrier on thesecond frequency using synchronization signals of the third carrier onthe third frequency.

According to still other embodiments of the present invention, a radioaccess network node may include radio frequency circuitry configured totransmit a first carrier including synchronization signals on a firstfrequency. In addition, a resource scheduler may be coupled to the radiofrequency circuitry, with the resource scheduler being configured totransmit information relating the first carrier on the first frequencywith a second carrier on the second frequency through the radiofrequency circuitry to a wireless terminal The resource scheduler mayalso be configured to transmit a command to add the second carrier onthe second frequency as a downlink for transmissions to the wirelessterminal, and the command to add the second carrier may be transmittedthrough the radio frequency circuitry to the wireless terminal. Thefirst and second frequencies are different, and the information isintended to be used in synchronization by the wireless terminal uponaddition of the second carrier.

According to yet other embodiments of the present invention, a wirelessterminal may be configured for communication with a radio access networkthat transmits a first carrier including synchronization signals on afirst frequency. The wireless terminal may include a processorconfigured to receive information relating a second carrier on a secondfrequency with the first carrier on the first frequency with theinformation being received from the radio access network. The processormay be further configured to receive a command to add the second carrieras a downlink for transmissions from the radio access network to thewireless terminal, and to synchronize and/or configure the secondcarrier on the second frequency using the synchronization signals of thefirst carrier on the first frequency responsive to receiving the commandto add the second carrier.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate certain embodiment(s) of theinvention. In the drawings:

FIG. 1 is a block diagram of a LTE RAN;

FIG. 2 illustrates a conventional resource grid of frequency and timeresource elements that can be scheduled for communication use between anetwork node and UEs;

FIG. 3 illustrates an exemplary LTE downlink radio frame that is dividedinto subframes;

FIG. 4 illustrates an exemplary Carrier Aggregation of ComponentCarriers;

FIGS. 5A and 5B illustrate an exemplary heterogeneous network havingthree cells that can cause severe inter-cell interference;

FIG. 6 illustrates one frequency reuse pattern that may be employed inthe exemplary heterogeneous network of FIG. 5;

FIGS. 7A and 7B illustrate some other frequency reuse patterns that maybe employed in the exemplary heterogeneous network of FIG. 5;

FIG. 8 illustrates a network that includes a macro antenna and a RemoteRadio Head (RRH) where two component carriers are time-aligned attransmission (time 0) but are no longer time-aligned at reception;

FIG. 9 illustrates a flowchart of exemplary operations and methods thatmay be carried out by a RAN to notify one or more terminals (UEs) of aSMCCL that should be used for synchronization of a SSCC;

FIG. 10 illustrates a flowchart of exemplary operations and methods thatmay be carried out by a terminal (UE) to perform aided synchronizationor individual synchronization;

FIG. 11 illustrates a flowchart of exemplary operations and methods thatmay be carried out by a RAN to notify one or more terminals (UEs) of aSSCCL;

FIG. 12 illustrates a flowchart of exemplary operations and methods thatmay be carried out by a terminal (UE) to perform aided synchronizationor individual synchronization; and

FIG. 13 is a block diagram of a portion of a RAN and a plurality of UEsthat are configured according to some embodiments of the presentinvention.

FIG. 14 illustrates a flow chart of exemplary operations and methodsthat may be carried out by a RAN to provide synchronization information.

FIG. 15 illustrates a flow chart of exemplary operations and methodsthat may be carried out by a terminal (UE) to provide synchronization.

DETAILED DESCRIPTION

The invention will now be described more fully hereinafter withreference to the accompanying drawings, in which embodiments of theinvention are shown. This invention may, however, be embodied in manydifferent forms and should not be construed as limited to theembodiments set forth herein; rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art.

For purposes of illustration and explanation only, various embodimentsof the present invention are described herein in the context ofoperating in a LTE RAN, such as the RAN 100 of FIG. 1. It will beunderstood, however, that the present invention is not limited to suchembodiments and may be embodied generally in any type of RAN that isconfigured to transmit and/or receive according to one or more RATs.

To mitigate one or more of the above-described problems, LTE Rel-10supports activation of CCs in addition to configuration of CCs. Theterminal monitors only PDCCH and PDSCH for configured and activated CCs.Since activation is based on Medium Access Control (MAC) controlelements—which are faster than RRC signaling—activation/de-activationcan follow the number of CCs that is required to fulfill the currentdata rate needs. Upon arrival of large data amounts multiple CCs areactivated, used for data transmission, and de-activated if not neededanymore. All but one CC—the DL Primary CC (DL PCC)—can be de-activated.Activation provides therefore the possibility to configure multiple CCbut only activate them on an as-needed basis. Most of the time aterminal would have one or very few CCs activated resulting in a lowerreception bandwidth and thus lower battery consumption.

It is to be understood that the present invention is not limited to theparticular terminology used herein. For example, the present inventionis not limited to the various terms that have been used to describe LTEcarrier aggregation, such as, Component Carriers (abbreviated CCs) andother terminology that is used in the above-description and by 3GPP fordefinition of the LTE standard. The present invention is furtherapplicable to, for example, RANs that are defined/described using termslike multi-cell or dual-cell operation, such as with a Primary ServingCell and potentially multiple Secondary Serving Cells, or the like.

A resource scheduler carries out scheduling of a CC on the PDCCH viadownlink assignments. Control information on the PDCCH is formatted as aDownlink Control Information (DCI) message. In Rel-8, a terminal onlyoperates with one DL and one UL CC, the association between DLassignment, UL grants and the corresponding DL and UL CCs is thereforeclear. In Rel-10, two modes of Carrier Aggregation need to bedistinguished. The first mode of operation is very similar to theoperation of multiple Rel-8 terminals in that a DL assignment or ULgrant contained in a DCI message transmitted on a CC is either valid forthe DL CC itself or for associated (either via cell-specific or UEspecific linking) UL CC. The second mode of operation augments a DCImessage with the Carrier Indicator Field (CIF). A DCI containing a DLassignment with CIF is valid for that DL CC indicted with CIF and a DCIcontaining a UL grant with CIF is valid for the indicated UL CC.

Carrier Aggregation in Heterogeneous Network Deployments:

Some embodiments of the present invention are directed to carriersynchronization for networks that provide carrier aggregation. Theseembodiments are described in the context of a heterogeneous networkhaving two cell layers, here referred to as “macro layer” and “picolayer”, respectively, although the invention is not limited to thatexemplary heterogeneous network, and other embodiments of the inventionmay be implemented in other networks (such as homogeneous networks). Nospecific assumptions are made regarding the characteristics of thedifferent cell layers. In some embodiments, the different cell layersmay correspond to cells having substantially different coverage areasizes (fundamentally defined by the coverage area of the basic controlsignals/channels, such as Primary Synchronization Channel, (PSS),Secondary Synchronization Channel (SSS), Physical Broadcast Channel(PBCH), Cell Specific Reference Signals (CRS), PDCCH, etc). In theexemplary heterogeneous network, a referenced “pico layer” can be amicro layer, a conventional outdoor or indoor pico layer, a layerconsisting of relays, or a Home eNB (HeNB) layer.

Various inter-cell interference scenarios may occur for co-channelheterogeneous network deployments. FIGS. 5A and 5B illustrate anexemplary heterogeneous network having three cells that can cause severeinter-cell interference. FIG. 5A illustrates how a HeNB may causeinterference towards a macro cell user that has no access to the femtocell (case (a)), and how a macro cell edge user may cause interferencetowards the HeNB due to no femto cell access (case (b)). FIG. 5Billustrates how interference from a macro eNB towards a pico cell (or afemto cell) edge user may increase (up to Δ) if path loss based servingcell selection is used instead of strongest received downlink signal.

The major inter-cell interference issues and concerns of co-channelheterogeneous network deployments in LTE refer to interference towardsresources that cannot rely on inter-cell interference coordination. Forschedulable data transmissions such as PDSCH and Physical Uplink SharedChannel (PUSCH), inter-cell interference can be coordinated via soft orhard physical resource partitioning, e.g. by exchanging coordinationinformation across layers/cells via the X2 interfaces.

It is desirable for legacy UEs to be able to operate and benefit fromheterogeneous network deployments, for example by accessing pico layersto improve uplink performance even if the received signal power from themacro layer is significantly higher. Such cell selection can beachieved, for example, by use of offset in Reference Signal ReceivedPower (RSRP) measurements carried out by the UE (corresponding to A inFIG. 5B). The current specification allows for an offset up to 24 dB,which should be sufficient for most heterogeneous network scenarios.

To mitigate severe downlink inter-cell interference from macro eNBstowards control regions of pico subframes, operating layers on differentcarriers may be necessary to ensure robust communications for legacy UEsin heterogeneous network deployments. However, such configurationimplies that the whole system bandwidth will not always be available forlegacy UEs and may result in reduced user throughputs. One example ofreduced throughput would be a split of a contiguous system bandwidth of20 MHz into two carriers, e.g. 10 MHz bandwidth on each carrier.

As explained above, operating different layers on differentnon-overlapping carrier frequencies may lead to resource-utilizationinefficiency. With the heterogeneous network illustration depicted inFIG. 6, this would imply that the overall available spectrum consists oftwo carriers f1 and f2, with f1 and f2 being exclusively used in themacro and pico layer, respectively. In the further explanation below, itis assumed that the layers are synchronized with time aligned eNBtransmissions and that f1 and f2 have non-overlapping frequency bands.

In many cases it can be assumed that the pico layer is deployed to carrythe main part of the traffic, and especially, provide the highest datarates, while the macro layer provides full-area coverage to fill anycoverage holes within the pico layer. In such a case it is desirablethat the full bandwidth, corresponding to carrier f1 and f2, isavailable for data transmission within the pico layer. It may also bedesirable for the full bandwidth (f1 and f2) to also be available fordata transmission within the macro layer, although the importance ofthis may be less than ensuring full-bandwidth availability in the picolayer.

As explained above, sharing of the resources (operation on the same setof carriers) between the cell layers for data transmission can beaccomplished by means of Inter-Cell Interference Coordination (ICIC)methods and operations that can be more or less dynamic depending on thecoordination capabilities between the layers and radio base stations. Apotentially key issue is to enable transmission of signals/channels thatcannot rely on traditional ICIC methods but need to be transmitted onspecific, well-defined, resources, including:

1) The synchronization signals (Primary Synchronization Channel(PSS)/Secondary Synchronization Channel (SSS));

2) The Physical Broadcast Channel (PBCH); and

3) L1/L2 control channels (Physical Downlink Control CHannel (PDCCH),Physical Control Format Indicator Channel (PCFICH) and PhysicalHybrid-ARQ Indicator Channel (PHICH)).

All these signals must be transmitted on at least one downlink carrierwithin each cell layer. It is assumed that this primary carriercorresponds to carrier f1 in the macro layer and carrier f2 in the picolayer.

For the downlink, three cases are shown in FIGS. 7A and 7B. Case 1differs from Case 2 (both shown in FIG. 7A) with respect to OpenSubscriber Group (OSG). In Case 3 (shown in FIG. 7C), both carriers, f1and f2, are available also at the macro layer. The three cases andexemplary operations and methods carried out by the associated RAN(e.g., by a resource scheduler therein, etc.) and UEs are furtherexplained below.

Case 1 of Carrier Aggregation in Heterogeneous Network Deployments:

Carrier f1 (the macro PCC) should be available for PDSCH transmissionalso within the pico layer. A UE is controlled to access the macro layerwhen the path loss to the macro layer is of the same order or smallercompared to the path loss to the pico layer.

In this case, the basic downlink control signals/channels above can betransmitted on f1 also in the pico layer with no severe interference toUEs accessing the macro layer. Thus both f1 and f2 can be deployed as“normal” (release 8 compatible) carriers in the pico layer. However, alegacy UE can access f1 only close to the pico cell site where the pathloss to the pico cell is much smaller than the path-loss to the macrocell, in order to avoid strong control-channel interference from themacro cell. Closer to the pico-cell border of the pico cell, Rel-10 UEsaccess on f2, to avoid strong interference to PSS/SSS and PBCH from themacro cell, but could be scheduled using PDSCH transmission on f1, usingcross-carrier scheduling with PDCCH on f2. Note that, to avoidinterference from macro Cell Specific Reference Signals (CRS), pico-cellPhysical Downlink Shared Channel (PDSCH) transmission on f1 must rely onUE-specific reference signals (RS) for channel estimation, at least whenthe UE is close to the pico-cell border. One might consider usingfrequency shifts of CRS across layers but macro CRS would then causeinterference towards the data resource elements of the pico.

Case 2 of Carrier Aggregation in Heterogeneous Network Deployments:

Similar to case 1, carrier f1 should be available for PDSCH transmissionalso within the pico layer. However, a UE should be configured to accessthe macro cell even when close to the pico cell.

This scenario may occur when the pico layer consists of HeNBs belongingto Closed Subscriber Groups (CSGs) and where a UE not belonging to theCSG approaches HeNB. In this case, the pico layer must not transmit thechannels above (PSS/SSS, Physical Broadcast CHannel (PBCH), CRS, PDCCH,etc.) on f1 in order to avoid interference to the UEs that are accessingthe macro layer in the vicinity of a pico site. Rather, thecorresponding resource elements should be empty. Thus, legacy UEs canonly access the pico layer on f2 while release 10 UEs can be scheduledon both f1 and f2 in the same way as for case 1.

Case 3 of Carrier Aggregation in Heterogeneous Network Deployments:

In addition to carrier f1 being available for PDSCH transmission withinthe pico layer, carrier 12 should be available for PDSCH transmissionwithin the macro layer.

In this case, the macro layer must not transmit the basic downlinksignals/channels above (PSS/SSS, PBCH, CRS, PDCCH, etc.) on f2 in orderto avoid interference to UEs that are accessing the pico layer and thatmay be in a location where signals from the macro layer are receivedwith much higher power, even though the path loss to the pico layer issubstantially smaller. Rather, similar to case 2, the correspondingresource elements should be empty. Thus, legacy UEs can only access themacro layer on f1 while Rel-10 UEs can be scheduled in the macro layeron both f1 and f2. It should be noted that a UE can only be scheduled onthe macro layer on f2 in such a way that it does not cause any severeinterference to the pico cell, either because there is no UE beingscheduled on the corresponding resource in any pico cell under thecoverage area of the macro cell or by using low power for the macro-celltransmission.

Note that, in the case where all pico cells are relatively far from themacro-cell site, the macro-cell site can be configured to also transmitthe basic control signals/channels (with reduced power on f2). However,this would make the macro-cell on f2 appear as a separate pico cell(located at the same point as the macro cell on f1).

Synchronization in Carrier Aggregation Systems:

Carrier aggregation in LTE Rel-10 is limited to aggregate backwardscompatible component carriers, i.e. each component carrier carries basicsignals like PSS/SSS, CRS, etc. However, as explained in the previoussection even though these signals may be present they can be transmittedwith zero/reduced power. Transmitting with zero power means the resourceelements for synchronization such as PSS/SSS, CRS, etc are reserved butmodulated with zero power.

In future releases even non-backwards compatible component carriers maybe aggregated and such carriers may not transmit PSS/SSS, CRS, etc atall. In other words, resource elements for synchronization signals maybe omitted from some component carriers according to some embodiments ofthe present invention.

PSSS/SSS and CRS can be used at the terminal to obtain synchronization.

Time-Alignment:

Depending upon whether all component carriers are transmitted from thesame site the received carriers may or may not be time-aligned. Forexample, if two or more component carriers are transmitted from the samesite and are time-aligned at the transmission side, they will also betime-aligned at reception. In case of intra-band carrier aggregation,tight requirements (i.e. within a fraction of the cyclic prefix) withrespect to time-alignment should occur in order to maintainorthogonality. For inter-band carrier aggregation, orthogonality isalready obtained due to the separation in frequency, so that no suchtight time-alignment requirements are needed.

However, when two or more component carriers are transmitted fromdifferent sites, configuring the sites to operate with co-alignment attheir transmitters does not guarantee time-alignment at reception. Forexample, FIG. 8 shows a Remote Radio Head (RRH) deployment where twocomponent carriers are time-aligned at transmission (time 0) but are nolonger time-aligned at reception. Accordingly, with reference to FIG. 8,although the transmissions from the macro antenna and the RRH antennaare time aligned at transmission, terminal UE1 is located closer to theRRH antenna than to the macro antenna and, therefore, it receives theRRH antenna transmission before it receives the macro antennatransmission. In contrast, terminal UE2 is located closer to the macroantenna than to the RRH antenna and, therefore, it receives the macroantenna transmission before it receives the RRH antenna transmission.Thus, when terminals will receive signals from multiple transmitterlocations, time alignment of the received signals cannot be assumed bythe terminal.

Potential Problems with Various Potential Signaling SynchronizationApproaches:

Typically the terminal uses PSS/SSS and/or CRS to synchronize. In Rel-10and later releases certain component carriers may not contain suchsynchronization signals or only contain synchronization signals withzero/reduced power, thus making synchronization using synchronizationsignals of those component carriers difficult or impossible.

Depending on the deployment scenario (common origin of componentcarriers vs. RRH) component carriers may be time-aligned or not. Since aterminal may not know in which scenario it is operating, time-alignmentof component carriers cannot be assumed, thereby making it potentiallyimpossible to blindly re-use the synchronization status of anothercomponent carrier.

Synchronization of component carriers can be achieved by relating (e.g.,correlating) the received carrier signal with the PSS/SSS and/or theCRS. However, when these signals are not present the terminal may beunable to achieve synchronization in that manner.

Operations and Methods of Various Embodiments of the Present Invention:

In accordance with various embodiments of the present invention,synchronization can be carried out in a carrier aggregation system whencomponent carriers are not transmitting or are transmitting withzero/reduced power PSS/SSS, CRS, etc. In some situations, thetransmission power of PSS/SSS and CRS on one CC may need to be reduced(or even set to zero) or eliminated in order to protect thecorresponding signals transmitted from another node. Moreover, componentcarrier types according to future specification may not even containPSS/SSS and CRS. In other words, resource elements for synchronizationsignals may be omitted from some component carriers according to someembodiments of the present invention. In other situations, a componentcarrier may include synchronization signals, but due to stronginterference from other cells, synchronization signals (e.g., PSS/SSSand/or CRS) may be difficult or impossible to receive.

In accordance with various embodiments of the present invention, the RANcommunicates to a terminal whether it should perform individualsynchronization of a component carrier using signals such as PSS/SSS/CRSon that component carrier or instead should perform aidedsynchronization, relying (partially) on the timing and frequency ofanother component carrier.

Before describing these embodiments, various further terminology usedherein will be defined. As used herein, “individual synchronization”refers to operations and methods performed by a terminal to synchronizeto a component carrier that provides signals needed for synchronization.In Rel-8/9, the individual synchronization signals can include PSS/SSSand/or CRS.

As used herein, “aided synchronization” refers to operations and methodsperformed by a terminal to synchronize to a component carrier that doesnot provide all signals (or provides the signals but with insufficientpower) required for individual synchronization. Thus, in order tosynchronize one component carrier, the terminal obtains aid from anothercomponent carrier. In one embodiment, the synchronization status (timeand/or frequency) are re-used from another component carrier.

As used herein, “Synchronization Master Component Carrier (SMCC)” refersto a component carrier that enables individual synchronization.

As used herein, “Synchronization Slave Component Carrier (SSCC)” refersto a component carrier that relies on aided synchronization.

As used herein, “Synchronization Master Component Carrier List (SMCCL)”refers to a list (SMCCL) that identifies all SMCC that can be used tosynchronize the SSCC. This list is specific for an SSCC, so another SSCCmay have a different SMCCL.

As used herein, “Synchronization Slave Component Carrier List (SSCCL)”refers to a list that identifies all SSCC that can use a SMCC for aidedsynchronization. This list is specific for an SMCC, so another SMCC mayhave a different SSCCL.

In accordance with some embodiments, synchronization of componentcarriers is facilitated by the network notifying the terminal as towhether it should perform individual synchronization of the componentcarrier or should instead perform aided synchronization.

As will be explained in further detail below, a RAN can be configured toidentify one or more CCs containing signals that can be used forsynchronization by a terminal. The RAN can generate a SMCCL and/or aSSCCL based on the one or more identified CCs and can communicate thegenerated SMCCL and/or SSCCL to the terminal. A terminal can becorrespondingly configured to receive an instruction from a RAN to add aCC and can determine whether a SMCCL and/or a SSCCL corresponding to theadded CC resides in the terminal, and can perform synchronization withrespect to the added CC responsive to that determination.

In accordance with first embodiments of the present invention, the RANincludes processor circuitry that is configured to identify to aterminal an SMCCL that is to be used for synchronization. For example,the terminal may be notified that component carrier n (SSCC) shouldperform aided synchronization using component carrier k (SMCC)identified in the SMCCL. If no SMCCL list has been provided to theterminal, then the terminal may be configured to carry out a defaultaction for synchronization. The default action can include performingindividual synchronization, where the component carrier actually doesnot rely on aided synchronization, or a default component carrier can beused for aided synchronization.

When there is only one SMCC, e.g. the PCC, the SMCCL can be defined by asingle bit indicating whether individual synchronization or aidedsynchronization is to be performed by the terminal. When aidedsynchronization is to be performed, a single SMCC is used. If no SMCCLis provided, the terminal can be configured to carry out a defaultsynchronization action.

FIG. 9 is a flowchart of exemplary operations 900 and methods that maybe carried out by a RAN (e.g., by control processor circuitry) to notifyone or more terminals (UEs) of a SMCC that should be used forsynchronization of a SSCC. It to be understood that one or more of theillustrated operations 900 may be omitted from at least some embodimentsof the present invention.

In the RAN, implementation of this embodiment can include, withreference to FIG. 9, configuring the eNB (e.g., via control processorcircuitry) to initiate a process at Block 910 to determine SMCCcandidates for SSCC synchronization by a terminal(s) responsive to, forexample, terminal acquisition of a cell and/or assignment of a new CC toa terminal. The eNB can access a local database at Block 920 thatcontains information, such as that identified below, that can be used togenerate a SMCCL as described herein. The eNB determines at Block 930which downlink component carriers contain signals that can be used by aterminal for synchronization. A further determination at Block 940 ismade as to which downlink component carriers will be time-aligned whenreceived at the terminal, where that determination can includedetermining time-alignment of a RRH relative to common origin andtransmission time.

For example the, control processor circuitry can be configured to accessa database residing at the eNB that identifies SMCCs that are candidatesfor use by a terminal for synchronization of one or more SSCCs. WhichSMCC(s) are preferably used by the terminal may be identified based onwhich component carriers contain signals that can be used by theterminal for synchronization, which component carriers are transmittedfrom a same transmission site (i.e., which component carriers are timealigned at transmission and/or having a known timing offset and willremain aligned or with the known timing offset when received by theterminal), which component carriers are transmitted from differenttransmission sites, and/or which component carriers a terminal isconfigured with.

Channel quality conditions that may affect one or more of the candidateSMCCs may also be determined at Block 950 (e.g., received signalstrength of one or more CCs measured at the terminal). The candidateSMCCs may be alternatively or additionally evaluated based on otherpredetermined or dynamically determined characteristics that can affectthe ability of the terminal to use a component carrier forsynchronization.

The RAN generates at Block 960 the SMCCL based on these determinations,and may generate one SMCCL that is common for all SSCCs or may generatedifferent SMCCLs for the different SSCCs.

Once the SMCCL(s) are generated, the RAN communicates at Block 970 theSMCCL to one or more terminals which associate the received SMCCL withthe SSCC. The RAN can transmit the SMCCL with dedicated signaling to theterminal and/or can distribute the SMCCL via broadcast. When the SMCCLis broadcasted, a terminal may receive the SMCCL before it is instructedto add the CC which is associated with the SMCCL. If dedicated signalingis used, the SMCCL may be part of the message instructing a terminal(UE) to add a new CC or the SMCCL may be transmitted in another message.

FIG. 10 is a flowchart of exemplary operations 1000 and methods that maybe carried out by a terminal (UE) to perform aided synchronization orindividual synchronization. It to be understood that one or more of theillustrated operations 1000 may be omitted from at least someembodiments of the present invention.

Referring to FIG. 10, a terminal responds at Block 1010 to instructionsfrom a RAN to add a component carrier by determining at Block 1020whether it has also received a corresponding SMCCL, which may have beenreceived via dedicated signaling and/or broadcast from the RAN. When theSMCCL is received via broadcast, the terminal may receive the SMCCLbefore it is instructed to add the CC which is associated with theSMCCL. If dedicated signaling is used, the SMCCL may be received as partof the message instructing the terminal (UE) to add a new CC or theSMCCL may be received in another message. When the terminal determinesthat it has a SMCCL associated with a SSCC, the terminal will thenperform aided synchronization for the SSCC using a SMCC that isidentified by the SMCCL at Block 1030. In contrast, when the terminaldetermines that it has not received a SMCCL that corresponds to a SSCCat Block 1040, the terminal may perform a default synchronizationaction. The default synchronization action can include performingindividual synchronization, where the terminal performs synchronizationto the component carrier without relying upon aid from another componentcarrier, or a default component carrier can be used for aidedsynchronization. For example, when a terminal has previously beenassigned first and second CCs, the terminal may then be further assigneda third CC and notified, via the SMCCL, to use the first CC or second CC(either one serving as a SMCC) for aided synchronization to the third CC(serving as a SSCC).

In accordance with second embodiments of the present invention, an SSCCLis provided for carriers that allow individual synchronization. TheSSCCL contains a list that identifies SSCCs that can use an associatedSMCC for aided synchronization.

FIG. 11 is a flowchart of exemplary operations 1100 and methods that maybe carried out by a RAN (e.g., by control processor circuitry) to notifyone or more terminals (UEs) of a SSCCL.

In the RAN, implementation of this embodiment can include, withreference to FIG. 11, configuring the eNB to initiate a process at Block1110 to notify a terminal of a SSCCL responsive to, for example,terminal acquisition of a cell and/or assignment of a new CC to aterminal. The eNB can access a local database at Block 1120 thatcontains information, such as that identified below, that can be used togenerate the SSCCL as described herein.

The eNB determines at Block 1130 which downlink component carrierscontain signals that can be used by a terminal for synchronization. Afurther determination at Block 1140 is made as to which downlinkcomponent carriers will be time-aligned when received at the terminal,where that determination can include determining time-alignment of a RRHrelative to common origin and transmission time.

For example, control processor circuitry can be configured to access adatabase residing at the eNB that identifies SMCCs that are candidatesfor use by a terminal for synchronization of one or more SSCCs. WhichSMCC(s) are preferably used by the terminal may be identified based onwhich component carriers contain signals that can be used by theterminal for synchronization, which component carriers are transmittedfrom a same transmission site (i.e., which component carriers are timealigned at transmission and/or have a known timing offset and willremain aligned or with the known timing offset when received by theterminal), and/or which component carriers are transmitted fromdifferent transmission sites.

Channel quality conditions that may affect one or more of the candidateSMCCs may also be determined at Block 1150 (e.g., received signalstrength of one or more CCs measured at the terminal), and/or based onother predetermined or dynamically determined characteristics that canaffect the ability of the terminal to use a component carrier forsynchronization.

The RAN generates at Block 1160 the SSCCL based on these determinations,and may generate one SSCCL that is common for all SMCCs or may generatedifferent SSCCL for the different SMCCs.

Once the SSCCL(s) are generated, the RAN communicates at Block 1170 theSSCCL to a terminal which associates the received SSCCL with the SMCC.The RAN can transmit the SSCCL with dedicated signaling to the terminaland/or can distribute the SSCCL via broadcast. When the SSCCL isbroadcasted, a terminal may receive the SSCCL before it is instructed toadd the SMCC which is associated with the SSCCL. If dedicated signalingis used, the SSCCL may be part of the message instructing a terminal(UE) to add the SMCC the SSCCL is associated with or the SMCCL may be(part of) another message.

FIG. 12 is a flowchart of exemplary operations 1000 and methods that maybe carried out by a terminal (UE) to perform aided synchronization orindividual synchronization. Referring to FIG. 12, a terminal responds atBlock 1210 to instructions from a RAN to add a component carrier bydetermining at Block 1220 whether it has also received a SSCCL, whichmay have been received via dedicated signaling and/or broadcast from theRAN and which contains the currently added component carrier.

When the SSCCL is received via broadcast, the terminal may receive theSSCCL before it is instructed to add the SMCC which is associated withthe SSCCL. If dedicated signaling is used, the SSCCL may be received aspart of the message instructing the terminal (UE) to add the SMCC theSSCCL is associated with or the SMCCL may be received in anothermessage. When the terminal determines that it has a SSCCL associatedwith a SMCC, the terminal will then perform aided synchronization forthe currently added component carrier using the SMCC the SSCCL belongsto at Block 1230.

In contrast, when the terminal determines that it does not possess aSSCCL that contains the currently added component carrier at Block 1240,the terminal may perform a default synchronization action. The defaultsynchronization action can include assuming that the currently addedcomponent carrier is an SMCC and performing individual synchronizationusing the currently added component carrier. In this case the terminalalso checks if the currently added SMCC has an SSCCL associated with it.

According to an alternate embodiment, an additional flag is included inan “add component carrier” command that is sent from the RAN to theterminal. This flag indicates whether the terminal should perform aidedsynchronization or not, independent of whether the terminal possesses anSSCCL that includes the currently added component carrier. In otherwords, this flag overwrites a potentially stored SSCCL. Accordingly,although the terminal may have an SSCCL that includes the currentlyadded component carrier, when the flag is set the terminal performsdefault synchronization, e.g. individual synchronization.

How the SMCCL and/or SSCCL lists are developed can depend upon, forexample, the deployment scenario (i.e., whether the component carriersare transmitted from a common transmission site origin or aretransmitted from multiple transmission sites, e.g., RRH) and whether thenetwork transmits channels on a component carrier that enablesindividual synchronization. Since these dependencies are rather static,using a semi-static signaling protocol, e.g. RRC signaling, may providecertain advantages. Moreover, because these SMCCL and/or SSCCL lists areoptional, in that they are not needed in all deployment scenarios,optional RRC Information Elements can be defined for SMCCL and SSCCL.

In this manner, various embodiments of the present invention can enablea terminal to perform synchronization in different deployment scenarios.The network performs various signaling that instruct the terminal toperform individual synchronization or to rely on aided synchronization.In the absence of these operational embodiments which enable terminalsynchronization where it would not otherwise be possible, a terminal mayeither not be able to perform network access or may perform networkaccess in a sub-optimum manner. Such sub-optimum network access couldinclude not being able to optimally utilize network resources, droppingcommunication connections, etc.

To avoid these potential problems, the network could either forbidmiss-alignment of received component carriers or forbid transmission ofPSS/SSS, CRS, etc with reduced power. However, forbidding miss-alignmentof received component carriers could prevent deployment of RRHs and/orsignificantly increase the operational complexity of that deployment.Forbidding transmission of PSS/SSS, CRS, etc with reduced/zero powercould make HetNet deployment sub-optimum. Since both deploymentscenarios can be important for future network deployments, these twoapproaches are likely not feasibly approaches.

FIG. 13 is a block diagram of a portion of a network node 1300 and UEs110-1 to 110-L that are configured according to some embodiments of thepresent invention. The network node 1300 may be provided as one or moreof the radio base station nodes (eNodeBs) of FIG. 1. Referring to FIG.13, the network node 1300 includes a resource scheduler 1330 that caninclude a resource element assignment processor 1332 and database 1334.The assignment processor 1332 may include one or more data processingand memory circuits, such as a general purpose and/or special purposeprocessor (e.g., microprocessor and/or digital signal processor) withon-board and/or separate memory device. The assignment processor 1332 isconfigured to execute computer program instructions from a memorydevice, described below as a computer readable medium, to assigncomponent carriers to the UEs 110-1 to 110-L and communicate thoseassignments thereto. Moreover, the assignment processor 1332 isconfigured to execute computer program instructions from a memory deviceto perform one or more of the operations 900 of FIG. 9 and/or one ormore of the operations 1100 of FIG. 11. The database 1134 containsinformation, such as the information described above regardingEmbodiment 1 and/or Embodiment 2, that can be used by the assignmentprocessor 1332 to generate SMCCLs and/or SSCCLs for communication to theUEs 110-1 to 110-L.

The network node 1300 includes RF circuitry 1320 having a plurality oftransceivers (TX/RX) 1322-1 to 1322-x that communicate using differentfrequency subcarriers through antennas 1324 a-n to provide the exemplarymultiple carrier portion of the resource grid shown in FIG. 2. Althoughan exemplary one-to-one mapping of transceivers to antennas is shown, itis to be understood that any number of antennas and/or transceivers maybe used depending upon antenna configuration and design constraints.

The network node 1300 can be configured to receive channel quality (CQ)reports and uplink (UL) buffer status reports from the UEs 110-1 to110-L. The uplink buffer status reports can indicate how many data bitsthe corresponding UE has buffered awaiting uplink transmission to theRAN 1300, and can be used by the assignment processor 1332 to identifywhich UEs require assignment of resource elements and determine how manyresource elements to assign to those UEs.

The CQ reports can indicate instantaneous downlink channel quality inboth time and frequency domain. The CQ reports can be used by theassignment processor 1332, for example, as described above for Block 950of FIG. 9 and Block 1150 of FIG. 11.

The network node 1300 can also include a plurality of radio link control(RLC) protocol buffers 1310-1 to 1310-M where downlink data that isreceived from the core network 130, via the interface (I/F) 1340, isbuffered awaiting transmission to addressed UEs. The assignmentprocessor 1332 can use RLC Buffer information to identify which UEsrequire assignment of resource elements and determine how many resourceelements to assign to those UEs.

Each of the UEs 110-1 to 110-L may include a processor 1312 and database1314. The processor 1312 may include one or more data processing andmemory circuits, such as a general purpose and/or special purposeprocessor (e.g., microprocessor and/or digital signal processor) withon-board and/or separate memory device. The processor 1312 is configuredto execute computer program instructions from a memory device, describedbelow as a computer readable medium, to perform aided synchronization orindividual synchronization according to at least some of the operations1000 of FIG. 10 and/or at least some of the operations 1200 of FIG. 12.The database 1314 can contain a listing of component carriers that havebe assigned to the UE by the assignment processor 1332 and contain alisting of associated SMCCL(s) and/or SSCCL(s) as explained above.

FIG. 14 is a flow chart illustrating operations of a network node 1300of FIG. 13, FIG. 15 is a flow chart illustrating operations of awireless terminal (such as user equipment 110-1 of FIG. 13), and takentogether, FIGS. 14 and 15 illustrate operations of network node 1300 anduser equipment providing signal synchronization according to someembodiments of the present invention. Operations of network node 1300and user equipment 110-1 will first be discussed together with referenceto FIGS. 14 and 15 to show interactions therebetween. Operations ofFIGS. 14 and 15 with then be discussed separately to clarify theseparate operations performed by network node 1300 and user equipment110-1.

In particular, RF circuitry 1320 of network node 1300 may be configuredto transmit an SMCC (Synchronization Master Component Carrier) includingsynchronization signals at Block 1410 on a first frequency. Thesynchronization signals, for example, may include PrimarySynchronization Channel signals, Secondary Synchronization Channelsignals, and/or Cell Specific Reference signals transmitted in periodicresource elements of the SMCC. According to some embodiments of thepresent invention, the SMCC may be configured and/or assigned as adownlink from RF circuitry 1320 to user equipment 110-1 before beingused by user equipment 110-1 to synchronize an SSCC on a differentfrequency. The SMCC, however, is not required to serve as a downlink touser equipment 110-1 before being used by user equipment to synchronizean SSCC.

Resource scheduler 1330 may make a determination to add an SSCC(Synchronization Slave Component Carrier) on a second frequency(different than the first frequency) to user equipment 110-1 at Block1420. Moreover, resource scheduler 1330 may relate one or more SMCC(s)(including the transmitted SMCC on the first frequency) with theassigned SSCC on the second frequency, and/or resource scheduler 1330may relate one or more SSCC(s) (including the assigned SSCC on thesecond carrier) with the transmitted SMCC on the first carrier at Block1430. As discussed above, this information relating SMCC(s) and SSCC(s)may be: a Synchronization Slave Component Carrier List (SSCCL) thatidentifies all SSCC(s) (including the SSCC on the second frequency to beadded) that can use the transmitted SMCC on the first frequency foraided synchronization; or a Synchronization Master Component CarrierList (SMCCL) that identifies all SMCC(s) (including the transmitted SMCCon the first frequency) that can be used to synchronize the SSCC on thesecond frequency to be added.

The information (e.g., SSCCL and/or SMCCL) relating the transmitted SMCCon the first frequency with the SSCC to be added on the second frequencymay be transmitted/received to/at user equipment 110-1 at Blocks 1440and 1510. More particularly, the information relating the transmittedSMCC and the SSCC to be added may be intended to be used forsynchronization by user equipment 110-1 upon addition of the SSCC. Inaddition, a command to add/configure the SSCC on the second frequency asa downlink may be transmitted/received to/at user equipment 110-1 atBlocks 1450 and 1520.

By relating SMCC(s) with SSCC(s) at Block 1430 for the particular userequipment 110-1 after the determination to add/configure the SSCC to/foruser equipment 110-1 at Block 1420, resource scheduler 1330 maydynamically relate SMCC(s) with SSCC(s) for specific user equipment110-1 based in part on a current location of user equipment 110-1,current signal strength/quality received at/from user equipment 110-1,time delays of signals received at/from user equipment 110-1, etc.According to some embodiments, resource scheduler 1330 may relateSMCC(s) and SSCC(s) transmitted from the same or different networknodes/antennas provided that the related SMCC(s) and SSCC(s) are timealigned at user equipment 110-1. With dynamic relation ofSMCC(s)/SSCC(s), for example, the information relating SMCC(s)/SSCC(s)may be transmitted at Block 1440 before, after, and/or concurrently withthe command to add/configure the SSCC at Block 1450 provided that theinformation is provided before user equipment 110-1 synchronizes theSSCC.

While FIGS. 14 and 15 illustrate a particular order of operations ofBlocks 1410, 1420, 1430, 1440, 1450, 1510, and 1520 according to someembodiments of the present invention, other orders of operations may beprovided according to other embodiments of the present invention.Resource scheduler 1330, for example, may statically relate SMCC(s) withSSCC(s) based on a location from which the SMCC(s) and SLCC(s) aretransmitted. Stated in other words, resource scheduler 1330 may relateSMCC(s) with SSCC(s) that are transmitted from a same antenna/location,because SMCC(s) and SSCC(s) transmitted from a same location may be timealigned (on reception) regardless of a location of the receiving userequipment 110-1. With statically related SMCC(s) and SSCC(s),information correlating SMCC(s) with SSCC(s) may be transmitted/receivedto/at user equipment 110-1 at Blocks 1440 and 1510, for example, beforethe determination to add the SSCC to user equipment 110-1 at Block 1420,or after the determination at Block 1420 as discussed above with respectto dynamic relation of SMCC(s)/SSCC(s).

According to some embodiments of the present invention, the SMCC on thefirst frequency may be configured and assigned as a downlink fromnetwork node 1300 to user equipment 110-1. Accordingly, transmitting theinformation relating the SMCC with the SSCC at Block 1440 may includetransmitting the information over the SMCC to user equipment 110-1,and/or transmitting the command to add the SSCC at Block 1450 mayinclude transmitting the command over the SMCC to user equipment 110-1.The information relating the SMCC with the SSCC, for example, may betransmitted at Block 1440 substantially concurrently with transmittingthe command to add the SSCC at Block 1450 over the SMCC on the firstfrequency.

According to some embodiments of the present invention, transmitting theinformation relating the SMCC with the SSCC at Block 1440 may includebroadcasting the information over a third frequency that is differentthan the first frequency of the SMCC and different than the secondfrequency of the SSCC. Such broadcast information may be made availablefor all user equipment 110 within range of the broadcast. Accordingly,the broadcast information relating SMCC(s) with SSCC(s) may bestatically determined based on locations/antennas from which the SMCC(s)and SSCC(s) are transmitted.

Responsive to receiving the information relating SMCC(s) with SSCC(s) atBlock 1510 and responsive to receiving the command to add the SSCC atBlock 1520, user equipment 110-1 may synchronize and/or configure theSSCC on the second frequency using synchronization signals from therelated SMCC on the first frequency at Block 1530. By relating the addedSSCC on the second frequency with a time aligned SMCC on the firstfrequency, user equipment 110-1 may synchronize the added SSCC withoutrequiring any synchronization signals to be provided/received over theSSCC. Accordingly, the SSCC may be transmitted without synchronizationsignals (e.g., the SSCC may be transmitted with synchronization resourceelements that are reserved but modulated with zero/low power, the SSCCmay actually be transmitted without synchronization signals, or the SSCCmay be transmitted without resource elements for synchronizationsignals).

User equipment 110-1 may transmit an acknowledgement to network node1300 at Block 1540 indicating that the SSCC on the second frequency hasbeen synchronized and/or configured at user equipment 110-1, and theacknowledgement may be received by network node 1300 Block 1460. Oncethe SSCC has been configured at Blocks 1460 and 1540, resource scheduler1330 may dynamically assign resource elements of the configured SSCC atBlock 1470 to provide downlink data transmission over the dynamicallyassigned resource elements 1490. Accordingly, user equipment 110-1 mayreceive the downlink data transmissions at Block 1550 using thedynamically assigned resource elements of the configured SSCC.

User equipment 110-1 may use the synchronization signals from therelated SMCC for the SSCC, for example, because: the SSCC may betransmitted without synchronization signals (e.g., the SSCC may betransmitted with synchronization resource elements that are reserved butmodulated with zero/low power, the SSCC may actually be transmittedwithout synchronization signals, or the SSCC may be transmitted withoutresource elements for synchronization signals); and/or synchronizationsignals of the SSCC may be subject to interference from a differentnetwork node/antenna transmitting on the same frequency as the SSCC.

In addition, network node 1300 may be configured to transmit a flag withthe command to add/configure the SSCC at Block 1450 to user equipment atBlock 1520, and the flag may have one of a first value and a secondvalue. The first value may instruct user equipment 110-1 to synchronizeand/or configure the second carrier using the synchronization signals ofthe first carrier as discussed above at Blocks 1440, 1450, 1460, 1520,1530, and 1540. The second value may instruct user equipment 110-1 tosynchronize and/or configure SSCC according to a default synchronizationwithout using the synchronization signals of SMCC. Accordingly, userequipment 110-1 may be configured to synchronize and/or configure thesecond carrier 1503 using the synchronization signals of the firstcarrier responsive to receiving the flag having the first value andsynchronizing and/or configuring the second carrier 1503 without usingthe synchronization signals of the first carrier responsive to receivingthe flag having the second value.

By way of example, a Primary Component Carrier (PCC) on a thirdfrequency (different than the first and second frequencies of the SMCCand the SSCC) may be configured as a downlink carrier for transmissionsfrom network node 1300 to user equipment 110-1, and the PCC may beconfigured before the command (to add/configure the SSCC) istransmitted/received to/at user equipment 110-1 at Blocks 1450 and 1520.Responsive to receiving the flag having the first value, user equipment110-1 may synchronize and/or configure the SSCC on the second frequencyusing the synchronization signals of the related SMCC on the firstfrequency. Responsive to receiving the flag having the second value,user equipment 110-1 may be configured to synchronize and/or configurethe SSCC on the second frequency using synchronization signals of thePCC on the third frequency.

According to other embodiments of the present invention, the command toadd/configure the SSCC may be transmitted using a carrier on a thirdfrequency (different than the first and second frequencies of the SMCCand the SSCC). Responsive to receiving the flag having the first value,user equipment 110-1 may synchronize and/or configure the SSCC on thesecond frequency using the synchronization signals of the related SMCCon the first frequency. Responsive to receiving the flag having thesecond value, user equipment 110-1 may synchronize and/or configure theSSCC on the second frequency using synchronization signals of the thirdcarrier on the third frequency. In other words, user equipment 110-1 mayuse synchronization signals of the carrier used to transmit the commandto synchronize and/or configure the SSCC.

According to yet other embodiments of the present invention, userequipment 110-1 may be configured to synchronize and/or configure theSSCC on the second frequency using the synchronization signals of therelated SMCC on the first frequency responsive to receiving the flaghaving the first value. Responsive to receiving the flag having thesecond value, user equipment 110-1 may synchronize and/or configure theSSCC on the second frequency using synchronization signals of the SSCCon the second frequency. In other words, the second value of the flagmay prompt user equipment 110-1 to synchronize and/or configure the SSCCusing its own synchronization signals. For example, the SSCC may betransmitted with synchronization resource elements that are modulatedwith low power, and resource scheduler 1330 may transmit the flag havingthe second value when user equipment 110-1 is sufficiently near networknode 1300 and/or subject to sufficiently low interference that the lowpower synchronization signals can be received and used.

Once user equipment 110-1 receives a command to add/configure a newSSCC, user equipment 110-1 may immediately time/frequency synchronizethe SSCC using the synchronization signals of the related SMCCresponsive to receiving the command, or user equipment 110-1 may wait toreceive an activation command before time/frequency synchronizing theSSCC using the synchronization signals of the related SMCC (responsiveto receiving the activation command). Once user equipment 110-1time/frequency synchronizes the added SSCC, user equipment 110-1 maymonitor a control channel (e.g., a Physical Downlink Control Channel orPDCCH) for the added SSCC for downlink assignments (used by resourcescheduler 1330 to assign SSCC resource elements for downlink datatransmissions). Responsive to receiving a downlink assignment for theadded SSCC from resource scheduler 1330, user equipment 110-1 mayreceive downlink data transmissions from network node 1300 over theassigned resource elements of the SSCC.

Operations of network node 1300 will now be discussed separately withrespect to the flow chart of FIG. 14 to clarify operations thereof. RFcircuitry 1320 of network node 1300 may be configured to transmit anSMCC (Synchronization Master Component Carrier) includingsynchronization signals at Block 1410 on a first frequency. Thesynchronization signals, for example, may include PrimarySynchronization Channel signals, Secondary Synchronization Channelsignals, and/or Cell Specific Reference signals transmitted in periodicresource elements of the SMCC. According to some embodiments of thepresent invention, the SMCC may be configured and/or assigned as adownlink from RF circuitry 1320 to user equipment 110-1 before beingused by user equipment 110-1 to synchronize an SSCC on a differentfrequency. The SMCC, however, is not required to serve as a downlink touser equipment 110-1 before being used by user equipment to synchronizean SSCC.

Resource scheduler 1330 may make a determination to add an SSCC(Synchronization Slave Component Carrier) on a second frequency(different than the first frequency) to user equipment 110-1 at Block1420. Moreover, resource scheduler 1330 may relate one or more SMCC(s)(including the transmitted SMCC on the first frequency) with theassigned SSCC on the second frequency, and/or resource scheduler 1330may relate one or more SSCC(s) (including the assigned SSCC on thesecond carrier) with the transmitted SMCC on the first carrier at Block1430. As discussed above, this information relating SMCC(s) and SSCC(s)may be: a Synchronization Slave Component Carrier List (SSCCL) thatidentifies all SSCC(s) (including the SSCC on the second frequency to beadded) that can use the transmitted SMCC on the first frequency foraided synchronization; or a Synchronization Master Component CarrierList (SMCCL) that identifies all SMCC(s) (including the transmitted SMCCon the first frequency) that can be used to synchronize the SSCC on thesecond frequency to be added.

The information (e.g., SSCCL and/or SMCCL) relating the transmitted SMCCon the first frequency with the SSCC to be added on the second frequencymay be transmitted to user equipment 110-1 at Block 1440. Moreparticularly, the information relating the transmitted SMCC and the SSCCto be added may be intended to be used for synchronization by userequipment 110-1 upon addition of the SSCC. In addition, a command toadd/configure the SSCC on the second frequency as a downlink may betransmitted to user equipment 110-1 at Block 1450.

By relating SMCC(s) with SSCC(s) at Block 1430 for the particular userequipment 110-1 after the determination to add/configure the SSCC to/foruser equipment 110-1 at Block 1420, resource scheduler 1330 maydynamically relate SMCC(s) with SSCC(s) for specific user equipment110-1 based in part on a current location of user equipment 110-1,current signal strength/quality received at/from user equipment 110-1,time delays of signals received at/from user equipment 110-1, etc.According to some embodiments, resource scheduler 1330 may relateSMCC(s) and SSCC(s) transmitted from the same or different networknodes/antennas provided that the related SMCC(s) and SSCC(s) are timealigned at user equipment 110-1. With dynamic relation ofSMCC(s)/SSCC(s), for example, the information relating SMCC(s)/SSCC(s)may be transmitted at Block 1440 before, after, and/or concurrently withthe command to add/configure the SSCC at Block 1450 provided that theinformation is provided before user equipment 110-1 synchronizes theSSCC.

While FIG. 14 illustrates a particular order of operations of Blocks1410, 1420, 1430, 1440, and 1450 according to some embodiments of thepresent invention, other orders of operations may be provided accordingto other embodiments of the present invention. Resource scheduler 1330,for example, may statically relate SMCC(s) with SSCC(s) based on alocation from which the SMCC(s) and SLCC(s) are transmitted. Stated inother words, resource scheduler 1330 may relate SMCC(s) with SSCC(s)that are transmitted from a same antenna/location, because SMCC(s) andSSCC(s) transmitted from a same location may be time aligned (onreception) regardless of a location of the receiving user equipment110-1. With statically related SMCC(s) and SSCC(s), informationcorrelating SMCC(s) with SSCC(s) may be transmitted to user equipment110-1 at Block 1440, for example, before the determination to add theSSCC to user equipment 110-1 at Block 1420, or after the determinationat Block 1420 as discussed above with respect to dynamic relation ofSMCC(s)/SSCC(s).

According to some embodiments of the present invention, the SMCC on thefirst frequency may be configured and assigned as a downlink fromnetwork node 1300 to user equipment 110-1. Accordingly, transmitting theinformation relating the SMCC with the SSCC at Block 1440 may includetransmitting the information over the SMCC to user equipment 110-1,and/or transmitting the command to add the SSCC at Block 1450 mayinclude transmitting the command over the SMCC to user equipment 110-1.The information relating the SMCC with the SSCC, for example, may betransmitted at Block 1440 substantially concurrently with transmittingthe command to add the SSCC at Block 1450 over the SMCC on the firstfrequency.

According to some embodiments of the present invention, transmitting theinformation relating the SMCC with the SSCC at Block 1440 may includebroadcasting the information over a third frequency that is differentthan the first frequency of the SMCC and different than the secondfrequency of the SSCC. Such broadcast information may be made availablefor all user equipment 110 within range of the broadcast. Accordingly,the broadcast information relating SMCC(s) with SSCC(s) may bestatically determined based on locations/antennas from which the SMCC(s)and SSCC(s) are transmitted.

Upon receiving an acknowledgement from user equipment 110-1 (indicatingsynchronization/configuration of the SSCC at user equipment 110-1) atnetwork node 1300 at Block 1460, resource scheduler 1330 may dynamicallyassign resource elements of the configured SSCC at Block 1470 to providedownlink data transmission over the dynamically assigned resourceelements 1490 to user equipment 110-1 at Block 1490.

Operations of user equipment 110-1 will now be discussed separately withrespect to the flow chart of FIG. 15 to clarify operations thereof.

In particular, the information (e.g., SSCCL and/or SMCCL) relating thetransmitted SMCC on the first frequency with the SSCC to be added on thesecond frequency may be received (from network node 1300) at userequipment 110-1 at Block 1510. More particularly, the informationrelating the transmitted SMCC and the SSCC to be added may be intendedto be used by user equipment 110-1 for synchronization upon addition ofthe SSCC. In addition, a command to add/configure the SSCC on the secondfrequency as a downlink may be received (from network node 1300) at userequipment 110-1 at Block 1520.

While FIG. 15 illustrates a particular order of operations of Blocks1510 and 1520 according to some embodiments of the present invention,other orders of operations may be provided according to otherembodiments of the present invention. With statically related SMCC(s)and SSCC(s), information correlating SMCC(s) with SSCC(s) may bereceived at user equipment 110-1 at Block 1510, for example, before orafter network node 1300 determines to add the SSCC to user equipment110-1.

According to some embodiments of the present invention, the SMCC on thefirst frequency may be configured and assigned as a downlink fromnetwork node 1300 to user equipment 110-1. Accordingly, receiving theinformation relating the SMCC with the SSCC at Block 1510 may includereceiving the information over the SMCC at user equipment 110-1, and/orreceiving the command to add the SSCC at Block 1520 may includereceiving the command over the SMCC at user equipment 110-1. Theinformation relating the SMCC with the SSCC, for example, may bereceived at Block 1510 substantially concurrently with receiving thecommand to add the SSCC at Block 1520 over the SMCC on the firstfrequency.

According to some embodiments of the present invention, receiving theinformation relating the SMCC with the SSCC at Block 1510 may includereceiving a broadcast of the information over a third frequency that isdifferent than the first frequency of the SMCC and different than thesecond frequency of the SSCC. Such broadcast information may beavailable for all user equipment 110 within range of the broadcast.Accordingly, the broadcast information relating SMCC(s) with SSCC(s) maybe statically determined based on locations/antennas from which theSMCC(s) and SSCC(s) are transmitted.

Responsive to receiving the information relating SMCC(s) with SSCC(s) atBlock 1510 and responsive to receiving the command to add the SSCC atBlock 1520, user equipment 110-1 may synchronize and/or configure theSSCC on the second frequency using synchronization signals from therelated SMCC on the first frequency at Block 1530. By relating the addedSSCC on the second frequency with a time aligned SMCC on the firstfrequency, user equipment 110-1 may synchronize the added SSCC withoutrequiring any synchronization signals to be provided/received over theSSCC. Accordingly, the SSCC may be transmitted without synchronizationsignals (e.g., the SSCC may be transmitted with synchronization resourceelements that are reserved but modulated with zero/low power, the SSCCmay actually be transmitted with no synchronization signals, or the SSCCmay be transmitted without resource elements for synchronizationsignals).

User equipment 110-1 may transmit an acknowledgement to network node1300 at Block 1540 indicating that the SSCC on the second frequency hasbeen synchronized and/or configured at user equipment 110-1. Once theSSCC has been configured at Block 1460, resource scheduler 1330 maydynamically assign resource elements of the configured SSCC to providedownlink data transmission over the dynamically assigned resourceelements 1490. Accordingly, user equipment 110-1 may receive thedownlink data transmissions at Block 1550 using the dynamically assignedresource elements of the configured SSCC. User equipment 110-1 may usethe synchronization signals from the related SMCC for the SSCC, forexample, because: the SSCC may be transmitted without synchronizationsignals (e.g., the SSCC may be transmitted with synchronization resourceelements that are reserved but modulated with zero/low power, the SSCCmay actually be transmitted with no synchronization signals, or the SSCCmay be transmitted without resource elements for synchronizationsignals); and/or synchronization signals of the SSCC may be subject tointerference from a different network node/antenna transmitting on thesame frequency as the SSCC.

In the above-description of various embodiments of the presentinvention, it is to be understood that the terminology used herein isfor the purpose of describing particular embodiments only and is notintended to be limiting of the invention. Unless otherwise defined, allterms (including technical and scientific terms) used herein have thesame meaning as commonly understood by one of ordinary skill in the artto which this invention belongs. It will be further understood thatterms, such as those defined in commonly used dictionaries, should beinterpreted as having a meaning that is consistent with their meaning inthe context of this specification and the relevant art and will not beinterpreted in an idealized or overly formal sense expressly so definedherein.

When an element is referred to as being “connected”, “coupled”,“responsive”, or variants thereof to another element, it can be directlyconnected, coupled, or responsive to the other element or interveningelements may be present. In contrast, when an element is referred to asbeing “directly connected”, “directly coupled”, “directly responsive”,or variants thereof to another element, there are no interveningelements present. Like numbers refer to like elements throughout.Furthermore, “coupled”, “connected”, “responsive”, or variants thereofas used herein may include wirelessly coupled, connected, or responsive.As used herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. Well-known functions or constructions may not be described indetail for brevity and/or clarity. The term “and/or” includes any andall combinations of one or more of the associated listed items.

As used herein, the terms “comprise”, “comprising”, “comprises”,“include”, “including”, “includes”, “have”, “has”, “having”, or variantsthereof are open-ended, and include one or more stated features,integers, elements, steps, components or functions but does not precludethe presence or addition of one or more other features, integers,elements, steps, components, functions or groups thereof. Furthermore,as used herein, the common abbreviation “e.g.”, which derives from theLatin phrase “exempli gratia,” may be used to introduce or specify ageneral example or examples of a previously mentioned item, and is notintended to be limiting of such item. The common abbreviation “i.e.”,which derives from the Latin phrase “id est,” may be used to specify aparticular item from a more general recitation.

Exemplary embodiments are described herein with reference to blockdiagrams and/or flowchart illustrations of computer-implemented methods,apparatus (systems and/or devices) and/or computer program products. Itis understood that a block of the block diagrams and/or flowchartillustrations, and combinations of blocks in the block diagrams and/orflowchart illustrations, can be implemented by computer programinstructions that are performed by one or more computer circuits. Thesecomputer program instructions may be provided to a processor circuit ofa general purpose computer circuit, special purpose computer circuit,and/or other programmable data processing circuit to produce a machine,such that the instructions, which execute via the processor of thecomputer and/or other programmable data processing apparatus, transformand control transistors, values stored in memory locations, and otherhardware components within such circuitry to implement thefunctions/acts specified in the block diagrams and/or flowchart block orblocks, and thereby create means (functionality) and/or structure forimplementing the functions/acts specified in the block diagrams and/orflowchart block(s).

These computer program instructions may also be stored in a tangiblecomputer-readable medium that can direct a computer or otherprogrammable data processing apparatus to function in a particularmanner, such that the instructions stored in the computer-readablemedium produce an article of manufacture including instructions whichimplement the functions/acts specified in the block diagrams and/orflowchart block or blocks.

A tangible, non-transitory computer-readable medium may include anelectronic, magnetic, optical, electromagnetic, or semiconductor datastorage system, apparatus, or device. More specific examples of thecomputer-readable medium would include the following: a portablecomputer diskette, a random access memory (RAM) circuit, a read-onlymemory (ROM) circuit, an erasable programmable read-only memory (EPROMor Flash memory) circuit, a portable compact disc read-only memory(CD-ROM), and a portable digital video disc read-only memory(DVD/BlueRay).

The computer program instructions may also be loaded onto a computerand/or other programmable data processing apparatus to cause a series ofoperational steps to be performed on the computer and/or otherprogrammable apparatus to produce a computer-implemented process suchthat the instructions which execute on the computer or otherprogrammable apparatus provide steps for implementing the functions/actsspecified in the block diagrams and/or flowchart block or blocks.

Accordingly, embodiments of the present invention may be embodied inhardware and/or in software (including firmware, resident software,micro-code, etc.) that runs on a processor such as a digital signalprocessor, which may collectively be referred to as “circuitry,” “amodule” or variants thereof.

It should also be noted that in some alternate implementations, thefunctions/acts noted in the blocks may occur out of the order noted inthe flowcharts. For example, two blocks shown in succession may in factbe executed substantially concurrently or the blocks may sometimes beexecuted in the reverse order, depending upon the functionality/actsinvolved. Moreover, the functionality of a given block of the flowchartsand/or block diagrams may be separated into multiple blocks and/or thefunctionality of two or more blocks of the flowcharts and/or blockdiagrams may be at least partially integrated. Finally, other blocks maybe added/inserted between the blocks that are illustrated. Moreover,although some of the diagrams include arrows on communication paths toshow a primary direction of communication, it is to be understood thatcommunication may occur in the opposite direction to the depictedarrows.

Many different embodiments have been disclosed herein, in connectionwith the above description and the drawings. It will be understood thatit would be unduly repetitious and obfuscating to literally describe andillustrate every combination and subcombination of these embodiments.Accordingly, the present specification, including the drawings, shall beconstrued to constitute a complete written description of variousexemplary combinations and subcombinations of embodiments and of themanner and process of making and using them, and shall support claims toany such combination or subcombination.

Many variations and modifications can be made to the embodiments withoutsubstantially departing from the principles of the present invention.All such variations and modifications are intended to be included hereinwithin the scope of the present invention.

That which is claimed is:
 1. A method of providing signalsynchronization for a radio access network, the method comprising:transmitting a first carrier including synchronization signals on afirst frequency from the radio access network; transmitting informationrelating the first carrier on the first frequency with a second carrieron a second frequency from the radio access network, said informationbeing intended to be used in synchronization by a wireless terminal uponaddition of the second carrier, wherein the first and second frequenciesare different; and transmitting a command to add the second carrier as adownlink for transmissions to the wireless terminal; whereintransmitting the command to add the second carrier comprisestransmitting a flag having one of a first value and a second value,wherein the first value instructs the wireless terminal to synchronizeand/or configure the second carrier using the synchronization signals ofthe first carrier, and wherein the second value instructs the wirelessterminal to synchronize and/or configure the second carrier withoutusing the synchronization signals of the first carrier.
 2. A methodaccording to claim 1 wherein the information relating the second carrierwith the first carrier comprises a list of a plurality of secondcarriers on a respective plurality of second frequencies that arerelated with the first carrier.
 3. A method according to claim 1 any ofwherein the first carrier is configured as a downlink to the wirelessterminal, and wherein transmitting the information relating the secondcarrier with the first carrier comprises transmitting the informationover the first carrier to the wireless terminal.
 4. A method accordingto claim 1 wherein transmitting the information relating the secondcarrier with the first carrier comprises transmitting the information tothe wireless terminal with the command to add the second carrier.
 5. Amethod according to claim 1 wherein transmitting the informationrelating the second carrier with the first carrier comprisestransmitting the information over a third frequency different than thefirst frequency and different than the second frequency.
 6. A methodaccording to claim 1 any of further comprising: after transmitting theinformation and the command to add the second carrier, receivingacknowledgment from the wireless terminal indicating synchronizationand/or configuration of the second carrier at the wireless terminal; andresponsive to receiving the acknowledgment, transmitting downlink dataover the second carrier to the wireless terminal.
 7. A method accordingto claim 1 wherein the synchronization signals are transmitted inperiodic resource elements of the first carrier.
 8. A method accordingto claim 1 wherein the first and second carriers are time aligned at thewireless terminal.
 9. A method of providing signal synchronization for aradio access network, the method comprising: transmitting a firstcarrier including synchronization signals on a first frequency from theradio access network; transmitting information relating the firstcarrier on the first frequency with a second carrier on a secondfrequency from the radio access network, said information being intendedto be used in synchronization by a wireless terminal upon addition ofthe second carrier, wherein the first and second frequencies aredifferent; and transmitting a command to add the second carrier as adownlink for transmissions to the wireless terminal; wherein the firstand second carriers are time aligned with each other.
 10. A methodaccording to claim 9 wherein transmitting the command to add the secondcarrier comprises transmitting a flag having one of a first value and asecond value, wherein the first value instructs the wireless terminal tosynchronize and/or configure the second carrier using thesynchronization signals of the first carrier, and wherein the secondvalue instructs the wireless terminal to synchronize and/or configurethe second carrier without using the synchronization signals of thefirst carrier.
 11. A method according to claim 9 wherein thesynchronization signals are transmitted in periodic resource elements ofthe first carrier.
 12. A method according to claim 9 wherein the firstand second carriers are time aligned at the wireless terminal.
 13. Amethod providing signal synchronization at a wireless terminal, saidwireless terminal communicating with a radio access network thattransmits a first carrier including synchronization signals on a firstfrequency, the method comprising: receiving, from the radio accessnetwork, information relating a second carrier on a second frequencywith the first carrier on the first frequency; receiving, from the radioaccess network, a command to add the second carrier as a downlink fortransmissions; and responsive to receiving the command to add the secondcarrier, synchronizing and/or configuring the second carrier on thesecond frequency using the synchronization signals of the first carrieron the first frequency; wherein receiving the command to add the secondcarrier comprises receiving a flag having one of a first value and asecond value, and wherein synchronizing and/or configuring the secondcarrier comprises synchronizing and/or configuring the second carrierusing the synchronization signals of the first carrier responsive toreceiving the flag having the first value and synchronizing and/orconfiguring the second carrier without using the synchronization signalsof the first carrier responsive to receiving the flag having the secondvalue.
 14. A method according to claim 13 wherein the informationrelating the second carrier with the first carrier comprises a list of aplurality of second carriers on a respective plurality of secondfrequencies that are related with the first carrier.
 15. A methodaccording to claim 13 wherein the first carrier is configured as adownlink from the radio access network to the wireless terminal, andwherein receiving the information relating the second carrier with thefirst carrier comprises receiving the information over the first carrierat the wireless terminal.
 16. A method according to claim 13 whereinreceiving the information relating the second carrier with the firstcarrier comprises receiving the information at the wireless terminalwith the command to add the second carrier.
 17. A method according toclaim 13 wherein receiving the information relating the second carrierwith the first carrier comprises receiving the information over a thirdfrequency different than the first frequency and different than thesecond frequency.
 18. A method according to claim 13 further comprising:before receiving the command, configuring a third carrier on a thirdfrequency as a downlink carrier for transmissions from the radio accessnetwork; responsive to receiving the flag having the first value,synchronizing and/or configuring the second carrier on the secondfrequency using the synchronization signals of the first carrier on thefirst frequency; and responsive to receiving the flag having the secondvalue, synchronizing and/or configuring the second carrier on the secondfrequency using synchronization signals of the third carrier on thethird frequency.
 19. A method according to claim 13 wherein thesynchronization signals are transmitted by the radio access network inperiodic resource elements of the first carrier.
 20. A method accordingto claim 13 wherein the first and second carriers are time aligned atthe wireless terminal.
 21. A method providing signal synchronization ata wireless terminal, said wireless terminal communicating with a radioaccess network that transmits a first carrier including synchronizationsignals on a first frequency, the method comprising: receiving, from theradio access network, information relating a second carrier on a secondfrequency with the first carrier on the first frequency; receiving, fromthe radio access network, a command to add the second carrier as adownlink for transmissions; and responsive to receiving the command toadd the second carrier, synchronizing and/or configuring the secondcarrier on the second frequency using the synchronization signals of thefirst carrier on the first frequency; wherein the first and secondcarriers are time aligned with each other.
 22. A method according toclaim 21 wherein receiving the command to add the second carriercomprises receiving a flag having one of a first value and a secondvalue, and wherein synchronizing and/or configuring the second carriercomprises synchronizing and/or configuring the second carrier using thesynchronization signals of the first carrier responsive to receiving theflag having the first value and synchronizing and/or configuring thesecond carrier without using the synchronization signals of the firstcarrier responsive to receiving the flag having the second value.
 23. Amethod according to claim 21 wherein the synchronization signals aretransmitted by the radio access network in periodic resource elements ofthe first carrier.
 24. A method according to claim 21 wherein the firstand second carriers are time aligned at the wireless terminal.
 25. Aradio access network node comprising: radio frequency circuitryconfigured to transmit a first carrier including synchronization signalson a first frequency; and a resource scheduler coupled to the radiofrequency circuitry, wherein the resource scheduler is configured totransmit information relating the first carrier on the first frequencywith a second carrier on the second frequency through the radiofrequency circuitry, and to transmit a command to add the second carrieron the second frequency as a downlink for transmissions to a wirelessterminal, wherein the command to add the second carrier is transmittedthrough the radio frequency circuitry to the wireless terminal, whereinthe first and second frequencies are different, said information beingintended to be used in synchronization by the wireless terminal uponaddition of the second carrier, and wherein the first and secondcarriers are time aligned with each other.
 26. A radio access networknode according to claim 25 wherein the resource scheduler is furtherconfigured to transmit the command to add the second carrier including aflag having one of a first value and a second value, wherein the firstvalue instructs the wireless terminal to synchronize and/or configurethe second carrier using the synchronization signals of the firstcarrier, and wherein the second value instructs the wireless terminal tosynchronize and/or configure the second carrier without using thesynchronization signals of the first carrier.
 27. A radio access networknode according to claim 25 wherein the first and second carriers aretime aligned at the wireless terminal.
 28. A wireless terminalconfigured for communication with a radio access network that transmitsa first carrier including synchronization signals on a first frequency,the wireless terminal comprising: a processor configured to receiveinformation relating a second carrier on a second frequency with thefirst carrier on the first frequency wherein the information is receivedfrom the radio access network, to receive a command to add the secondcarrier as a downlink for transmissions from the radio access network tothe wireless terminal, and to synchronize and/or configure the secondcarrier on the second frequency using the synchronization signals of thefirst carrier on the first frequency responsive to receiving the commandto add the second carrier, wherein the first and second carriers aretime aligned with each other.
 29. A wireless terminal according to claim28 wherein the processor is configured to receive the command to add thesecond carrier by receiving a flag having one of a first value and asecond value, and wherein the processor is configured to synchronizeand/or configure the second carrier by synchronizing and/or configuringthe second carrier using the synchronization signals of the firstcarrier responsive to receiving the flag having the first value and bysynchronizing and/or configuring the second carrier without using thesynchronization signals of the first carrier responsive to receiving theflag having the second value.
 30. A wireless terminal according to claim28 wherein the first and second carriers are time aligned at thewireless terminal.